Local IMS selection for trusted network operators

ABSTRACT

A first carrier may support inbound roaming requests for subscribers of a trusted second carrier. For example, the first carrier may receive an inbound roaming request from a UE. The first carrier may determine a second carrier that is a home carrier of the UE is a trusted carrier associated with the first carrier. In response, an IMS procedure associated with the UE may be performed including communicating, by a first CSCF node of the first carrier, with a first HSS of the second carrier, using a same protocol as used by the first CSCF node to communicate with a second HSS of the first carrier and communicating, by the first CSCF node, with a first AS of the second carrier, using a same protocol as used by the first CSCF node to communicate with a second AS of the first carrier.

BACKGROUND

Modern cellular communication networks often include IP MultimediaSubsystems (IMSs) for delivering IP multimedia services. In manysituations, however, users who are attempting to communicate with eachother may be supported by different communication providers, so thatmultimedia calls and communications need to be set up between IMSsystems.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is described with reference to the accompanyingfigures. In the figures, the left-most digit(s) of a reference numberidentifies the figure in which the reference number first appears. Theuse of the same reference numbers in different figures indicates similaror identical components or features.

FIG. 1 is a block diagram illustrating a communication system thatincludes multiple IMS networks operated by different communicationproviders.

FIG. 2 is a flow diagram illustrating an example method of processing anIMS roaming request in the example system of FIG. 1 .

FIG. 3 is a flow diagram illustrating an example method of processing anIMS roaming request in the example system of FIG. 1 .

FIG. 4 is a flow diagram illustrating an example method of handinginbound roaming requests.

FIG. 5 is a block diagram illustrating relevant high-level components ofa device that may be used to implement various of the componentsdescribed herein.

DETAILED DESCRIPTION

The described implementations provide devices, systems, and methods thatallow local IMS selection to be provided between IP multi-mediasubsystems (IMSs) of different communication providers or carriers, andparticularly between trusted carriers. In certain described embodiments,the devices, systems, and methods disclosed herein relate to providingIMS services for a roaming subscriber of another trusted carrier. Insome examples, a trusted partner carrier of a carrier may be anothercarrier which is merging with the particular communication provider butwhose user equipment has not migrated to the subscriber identity module(SIM) of the particular carrier. Local IMS selection may provide aflexibility to integrate two carriers with ease of migration of trafficduring integration procedures without adversely impacting theprovisioning and/or charging architecture for the carriers. In otherexamples, two non-merging carriers may agree to a trusted relationshipin which they share networks without changing their SIM systems. Instill other examples, two networks associated with the same carrier withdifferent SIM systems (e.g. a first network of the carrier in the UnitedStates and a second network of the carrier in the Europe which havedifferent SIM systems) may utilize Local IMS selection to reducecomplexity and costs associated with subscribers roaming between thenetworks.

In embodiments described herein, the IMS of a carrier may include one ormore call session control functions (CSCFs) that may be responsible forcoordinating incoming requests with the IMS cores of trusted partnercarriers. In some cases, the one or more call session control functions(CSCFs) may include interfaces with at least one of the home subscriberserver (HSS) and an Application Server (AS) (e.g. a TelephonyApplication Server (TAS)) of the trusted partner carrier. For example,the one or more call session control functions (CSCFs) may include oneor more Diameter (e.g. Cx) interfaces with the HSS of the trustedpartner carrier and one or more IP multimedia Subsystem Service ControlInterfaces (ISC) with the TAS of the trusted partner carrier.

In some cases, the carrier may also include other systems (e.g. controlfunctions) for coordinating incoming requests with the IMS cores ofother (e.g. non-trusted) carriers such as breakout gateway controlfunctions (BGCFs), interconnect border control functions (IBCFs), MediaGateway Control Functions (MGCFs). For example, incoming requests for aroaming subscriber of a non-trusted other carrier may be handled via acircuit switched network by one or more of a BGCF, a IBCF, a MGCF and aI-SBC of the carrier and similar systems of the non-trusted othercarrier.

FIG. 1 illustrates an example telecommunication system 100, which may beprovided and/or supported by multiple carriers. The system 100 includesa carrier 1 (C1) 102, a trusted partner carrier 2 (C2) 104, and anon-trusted carrier 3 (C3) 106 which interface to provide service to auser equipment (UE) 108. In particular, carriers 102-106 may providecommunications between multiple user equipment (UE) devices (referred tosimply as UE in the following discussion). Communications may be betweenUEs of the same carrier (also referred to herein as service provider)and/or may be between UEs supported by different carriers. In thisexample, the illustrated UE 108 may be a subscriber of carrier 2 104.Further, the illustrated UE 108 may be roaming in a service area ofcarrier 1 102 while attempting to obtain communication services.

Carrier 1 102 may provide communications services to user equipmentsupported by other carriers (e.g. roaming subscribers such as UE 108),referred to as partners, which may comprise other cellular providers orservice providers. In some implementations, depending on therelationship between the carriers, the IMS 110 of the carrier 1 102 maycommunicate with a corresponding IMS of the partner through varioustypes of media, control functions and gateways. The IMSs of the partnerwill be referred to as partner IMSs herein.

The carriers 1-3 102-106 have various components, of which only thosemost relevant to the current discussion are shown in FIG. 1 .

As shown herein, the carrier 1 102 may include a mobility managemententity (MME) 112, a signaling gateway (SGW) 114, a IMS Packet DataNetwork Gateway (PGW) 116, a Proxy-Call Session Control Function(P-CSCF) 118, an I/S-CSCF 120 (e.g. an Interrogating-Call SessionControl Function (I-CSCF) and a Serving-Call Session Control Function(S-CSCF)), an HSS 122, a TAS 124, a BGCF 126, an E.164 Number to URIMapping (ENUM) 128, and a carrier 1 circuit switched network (C1-CS)130. Carrier 2 104 may include, in pertinent part, a HSS 132, a TAS/IMP134 and an I/S-CSCF 136. Finally, carrier 3 106 may include, inpertinent part, a carrier 3 circuit switched network (C3-CS) 138 and acarrier 3 IMS (C3-IMS) 140. Depending on the implementation, eachcircuit switched network may include one or more of an IBCF, a MGCF andan I-SBC.

As mentioned above, the manner in which roaming services are handled bycarrier 1 102 may vary based on the relationship between the carriers102-106. In the case that carrier 1 102 has a trusted relationship withthe home carrier of a roaming subscriber (e.g. carrier 2 104), the IMS110 may include one or more call session control functions (CSCFs) thatmay be responsible for coordinating incoming requests with the IMS coresthe trusted partner IMSs of such trusted partner carriers. On the otherhand, incoming requests for the roaming subscribers of non-trustedcarriers (e.g. carrier 3 106) may be handled via a circuit switchednetwork by one or more of a BGCF, a IBCF, a MGCF and a I-SBC of carrier1 102 and similar systems of the non-trusted carrier. Additional detailsregarding roaming services are provided below. The IMS 110 maycommunicate with the carriers 104 and 106 over various type of networks,including wired and/or wireless networks, and including private and/orpublic networks.

The IMS 110 may support various types of communication and mediaservices. In the illustrated example, the IMS 110 includes a telephonyaccess server 124 that provides voice communication services. The IMSmay also include or support other functions such as an IP short messagegateway (IP-SM-GW), which is a service for communicating short messages,such as short message service (SMS) over IP (SMSIP) messages, betweenUEs. The IMS 110 also may include or support the Rich CommunicationSuite (RCS), which is a platform that supports various types of mediacommunications, including one-to-one chat, group chat, file transfer,content sharing, voice calling, video calling, social presence, videocalling, geolocation exchange, service identification, notifications,and others. Each of these services may be implemented by one or morecorresponding application servers that form part of the IMS 110.

The UE 108 comprises a communication device configured to communicateover a wireless and/or wireline network, including, without limitation,a mobile phone (e.g., a smart phone), a tablet computer, a laptopcomputer, a portable digital assistant (PDA), a wearable computer (e.g.,electronic/smart glasses, smart watches, fitness trackers, etc.), anetworked digital camera, etc. The UE 108 may also comprise a non-mobilecomputing device. Examples of non-mobile UEs may include such things astelevisions, desktop computers, a game consoles, set top boxes, homeautomation components, security system components, and so forth. In thissense, the terms “communication device,” “wireless device,” “wirelinedevice,” “mobile device,” “computing device,” and “user equipment (UE)”may be used interchangeably herein to describe any communication devicecapable of performing the techniques described herein.

Furthermore, the UE 108, as well as the various network providercomponents described herein, may be capable of communicating over wirednetworks, and/or wirelessly using any suitable wirelesscommunications/data technology, protocol, or standard, such as GlobalSystem for Mobile Communications (GSM), Time Division Multiple Access(TDMA), Universal Mobile Telecommunications System (UMTS),Evolution-Data Optimized (EVDO), Long Term Evolution (LTE), Advanced LTE(LTE+), Generic Access Network (GAN), Unlicensed Mobile Access (UMA),Code Division Multiple Access (CDMA), Orthogonal Frequency DivisionMultiple Access (OFDM), General Packet Radio Service (GPRS), EnhancedData GSM Environment (EDGE), Advanced Mobile Phone System (AMPS), HighSpeed Packet Access (HSPA), evolved HSPA (HSPA+), Voice over IP (VoIP),Voice over LTE (VoLTE), IEEE 802.1x protocols, WiMAX, Wi-Fi, and/or anyfuture IP-based network technology or evolution of an existing IP-basednetwork technology. These are merely examples and the UE 108, as well asthe various network provider components described herein, may be capableof communicating via one or more of a 3G, 4G, 4G LTE, and/or 5Gprotocols.

The UE 108 communicates with the IMS 110 using an access network (notshown), which may comprise a cellular communication network or othertype of wired or wireless network. Examples of wireless access networksinclude LTE, WIFI, GSM EDGE Radio Access Network (GERAN), UMTSTerrestrial Radio Access Network (UTRAN), and other cellular accessnetworks.

The UE 108 may be configured to initiate a communication session, suchas a voice call, a video call, or another sort of synchronous orasynchronous communication. Initiation of such communications mayinvolve communication clients and session initiation protocol (SIP)clients to communicate with components of the carrier 1 102.

More particularly, the UE 108 may be configured to initiatecommunication with the mobility management entity (MME) 112 of thecarrier 1 102. The MME 112 may interact with the UE 108 in an attachmentprocess.

In the case of a roaming subscriber of a trusted partner (e.g. UE 108),the MME 112 may direct the roaming traffic of the UE via a signalinggateway (SGW) 114 to a IMS Packet Data Network Gateway (PGW) 116 that isassigned to handle the IMS VoLTE Access Point Name (APN) of the trustedpartner (e.g. carrier 2). The IMS PGW 116 can select a P-CSCF 118 withinthe IMS 110 of carrier 102 to handle the IMS request procedure for theinbound roaming subscriber of the trusted partner (e.g. UE 108) viaI/S-CSCF 120. More particularly, the P-CSCF 118 may route the IMSrequest to one or more I/S-CSCFs that are assigned to handlecommunications with subscribers of trusted partners. In implementationsaccording to this disclosure, the I/S-CSCF 120 may support multiplecarriers or realms (e.g. interface with the HSS and AS of multiplecarriers or realms). In addition or alternatively, each I/S-CSCF 120 mayhave one or more assigned trusted partners and the P-CSCF 118 may routethe IMS request to the I/S-CSCF 120 based on the trusted partner.

In the illustrated example, the I/S-CSCF 120 may interface with the HSS122 and TAS 124 of carrier 1 102 over a diameter Cx interface and a ISCinterface, respectively. In addition, the I/S-CSCF 120 may interfacewith the HSS 132 and TAS/IMP 134 of carrier 2 104 over a diameter Cxinterface and a ISC interface, respectively. In turn, the HSS 132 andTAS 134 may whitelist the I/S-CSCF 120 for Cx and ISC interfaces,respectively. In some examples, the I/S-CSCF 120 may further include aMw interface to the I/S-CSCF 136 of the carrier 2 104. Though not shownfor ease of understanding and illustration, in some implementations, theI/S CSCF 120 may include interfaces (e.g. Cx and ISC interfaces) to theHSS and TAS/IMP within the IMSs of multiple trusted partners or trustedcarriers in addition to carrier 2 104.

Using the Cx interface with the HSS 132 of carrier 2 104, the I/S-CSCF120 may interact with the HSS 132 of the trusted partner (e.g. carrier104) that is the home carrier of the UE 108 for authorization (e.g. toobtain user authentication information associated with the UE 108) andserver assignment procedures. For example, the I/S CSCF 120 may downloadinitial Filter Criteria's (iFCs) of the roaming subscriber's AS (e.g.TAS/IMP 134) for IMS services. The I/S-CSCF 120 may then interact withthe TAS/IMP 134 of carrier 2 104 using the ISC interface therewith toobtain IMS services from the TAS/IMP 134. In some examples, using thecross realm Cx and ISC interfaces as described herein may allow carriersto reduce complexity between the trusted partners. Further, having thecarrier 1 102 serve as call control may provide consolidated callrouting with other carriers which may provide cost and resource savings.Moreover, the charging and provisioning logic may reside in the homenetwork of the UE 108 (e.g. C2 104) while the call control functions arehandled by the roaming network (e.g. C1 102) without failing to supportthe features supported in the home network of the UE 108 (e.g. C2 104).

In some implementations, the inbound IMS request may originate fromanother UE. For example, a second UE on carrier 2 104 or carrier 3 106may originate the IMS request. For example, the I/S CSCF 136 may forwarda request relating to a call between the UE 108 and a second UE on thecarrier 2 104 to the I/S-CSCF 120. In response and in a similar mannerto that discussed above, the I/S-CSCF 120 may use the Cx and ISCinterfaces with the HSS 132 and TAS/IMP 134 of carrier 2 104 toestablish call control and other functions for the call.

In the case of a roaming subscriber of a non-trusted carrier, the MME112 may direct the roaming traffic of the UE via a signaling gateway(SGW) to a IMS Packet Data Network Gateway (PGW) that is assigned tohandle communication with IMS VoLTE Access Point Name (APN) ofnon-trusted carrier (e.g. carrier 2).

More particularly, incoming requests for the roaming subscribers ofnon-trusted carriers (e.g. carrier 3 106) may be handled via the circuitswitched network C1-CS 130 by the BGCF 126 and ENUM 128 in conjunctionwith similar systems of the non-trusted carrier (e.g. the circuitswitched network C3-CS 138 and C3-IMS 140 of carrier 3 106). Moreparticularly, the I/S-CSCF 120 may call the ENUM 128 to determine thedomain or host name of a home carrier (e.g. C3 106) of the roamingsubscriber UE. The IMS requests may then be handled by the BGCF 126 viathe C1-CS 130 in conjunction the C3-CS 138 and C3-IMS 140 of carrier 3106.

FIG. 2 illustrates an example method 200 of processing an IMS request inthe example system of FIG. 1 , according to some implementations. In theillustrated example, the data flow relates to the IMS request of aroaming subscriber (e.g. UE 108) whose home carrier (e.g. C2 104) has atrusted relationship with the visited carrier (e.g. C1 102). Moreparticularly, the illustrated example of FIG. 2 includes the UE 108calling a subscriber of C1 102. To illustrate the separate operations ofthe S-CSCF and I-CSCF of I/S-CSCF 120, the S-CSCF is labeled as S-CSCF120A and the I-CSCF is labeled as I-CSCF 120B.

Prior to the data flow shown in FIG. 2 , the UE 108 may register in theroaming network (e.g. carrier 1 102), during which the HSS 132 ofcarrier 2 104 may be involved. For example, the I-CSCF 120B may downloadthe authentication vectors for authorization of the UE 108. The S-CSCF120A may then download the iFCs from the HSS 132 of the carrier 2 104and may implement actions based on the iFCs (i.e. to reach out to ASslike TAS/IMP 134 for third party registration). Immediately prior to thedata flow of FIG. 2 , the P-CSCF 118 may receive a MO INVITE from the UE108.

At 202, the P-CSCF 118 may forward a received MO INVITE to the S-CSCF120A. At 204, the S-CSCF 120A may send the INVITE to the TAS/IMP 134 ofthe second carrier (e.g. C2 104, the home carrier of the UE 108) fororiginating voice services.

The TAS/IMP 134 may handle originating the services. The TAS/IMP 134 maythen send the INVITE back to the S-CSCF 120A at 206.

At 208, the S-CSCF 120A may perform an ENUM inquiry on the called numberwith the ENUM 128. The ENUM may respond with the domain of the carrierof the called party. In the illustrated example, in the ENUM response at210, the S-CSCF 120A may receive the domain of carrier 1 102 (e.g.because the called party is a subscriber of carrier 1 in this example).

At 212, based on ENUM response, the S-CSCF 120A may send the INVITEtowards the I-CSCF 120B for handling the call termination using thedomain of carrier 1 102.

More particularly, at 214, the I-CSCF 120B may select the HSS 122 of thecarrier 1 102 based on the returned domain of the terminating user. TheI-CSCF 120B may then perform a Cx interface procedure with the HSS 122of the carrier 1 102 network to determine the S-CSCF to use for the calltermination. In this case, the HSS 122 may determine the S-CSCF 120A tobe the S-CSCF to handle call termination and interaction with the TAS124. The HSS 122 may include this information in a response at 216.Based on the HSS 122 response, the I-CSCF 120B may return the INVITE tothe S-CSCF 120A at 218.

At 220, the S-CSCF 120A may send the INVITE to the serving terminatingTAS (e.g. TAS 124) for terminating voice services. The TAS 124 mayprocess the INVITE for call termination for the called party and thensend the INVITE back to S-CSCF 120A at 222.

Finally, at 224, the S-CSCF 120A may send the INVITE to the terminatingP-CSCF of carrier 1 102 (e.g. P-CSCF 118) for relaying to the calledparty UE.

Although FIG. 2 has been discussed in the context of an incoming IMSrequest being received from within the carrier 1 102 and/or from a UE108 that is associated with and supported by carrier 2 104, the same orsimilar actions may be performed with respect to an inbound roamingrequest that is received from a partner carrier 104.

Note also that while the techniques described above are described asbeing implemented by particular CSCFs, the described techniques mayalternatively be implemented by any one or more other components of thecarrier 1 102 as may be appropriate depending on the particularimplementation.

FIG. 3 illustrates an example method 300 of processing a IMS request inthe example system of FIG. 1 , according to some implementations. In theillustrated example, the data flow relates to the IMS request of aroaming subscriber (e.g. UE 108) whose home carrier (e.g. C2 104) has atrusted relationship with the visited carrier (e.g. C1 102). Moreparticularly, the illustrated example of FIG. 3 includes the UE 108calling another subscriber of C2 104 that is also roaming on the C1 102network. As with FIG. 2 , to illustrate the separate operations of theS-CSCF and I-CSCF of I/S-CSCF 120, the S-CSCF is labeled as S-CSCF 120Aand the I-CSCF is labeled as I-CSCF 120B. Prior to the data flow shownin FIG. 3 , the P-CSCF 118 receives a MO INVITE from the UE 108.

At 302, the P-CSCF 118 may forward a received MO INVITE to the S-CSCF120A. At 304, the S-CSCF 120A may send the INVITE to the TAS/IMP 134 ofthe second carrier (e.g. C2 104, the home carrier of the UE 108) fororiginating voice services.

The TAS/IMP 134 may handle originating the services. The TAS/IMP 134 maythen send the INVITE back to S-CSCF 120A at 306.

At 308, the S-CSCF 120A may perform an ENUM inquiry on the called numberwith the ENUM 128. In the ENUM response at 310, the S-CSCF 120A mayreceive the domain of carrier 2 104 (e.g. because the called party is asubscriber of carrier 2 104 in this example).

At 312, based on ENUM response, the S-CSCF 120A may send the INVITEtowards the I-CSCF 120B for handling the call termination using thedomain of carrier 2 104.

More particularly, at 314, the I-CSCF 120B may perform a Cx interfaceprocedure with the HSS 132 of the carrier 2 104 network to determine theS-CSCF to use for the call termination. In this case, the HSS 132 maydetermine the S-CSCF 120A to be the S-CSCF to handle call terminationand interaction with the TAS 134. The HSS 132 may include thisinformation in a response at 316. Based on the HSS 132 response, theI-CSCF 120B may return the INVITE to the S-CSCF 120A at 318.

At 320, the S-CSCF 120A may send the INVITE to the terminating TAS (e.g.TAS 134 of C2 104) for terminating voice services. The TAS 134 mayprocess the INVITE for call termination for the called party and thensend the INVITE back to S-CSCF 120A at 322.

Finally, at 324, the S-CSCF 120A may send the INVITE to the terminatingP-CSCF of carrier 1 102 (e.g. P-CSCF 118) for relaying to the calledparty UE.

FIG. 4 illustrates an example method 400 of processing an inboundroaming request, according to some implementations.

At 402, a first carrier network receives an inbound roaming request froma user equipment (UE). The first carrier network then determines whethera second carrier network that is a home carrier network of the UE is atrusted carrier network associated with the first carrier network at404. In a non-limiting example, a carrier network may be a trustedcarrier network associated with the first carrier network when the twonetworks are integrating with each other on the roadmap to become singlenetwork. If so (e.g. trusted), at 406, the first carrier network opts touse local IMS selection and provides the inbound roaming request to afirst CSCF node of the first carrier network and the process continuesto 408. Otherwise (e.g. not trusted), at 406, the first carrier networkmay opt to use another procedure for the inbound roaming request and theprocess continues to 410.

At 408, the first CSCF node may handle the inbound roaming request. Forexample, a local I/S-CSCF may handle the inbound roaming request via aninterface with the HSS and the TAS of the second carrier network. Moreparticularly, the first CSCF node may perform an IMS request procedureassociated with the UE at least by communicating with a first HomeSubscriber Server (HSS) of the second carrier network, using a sameprotocol as used by the first CSCF node to communicate with a second HSSof the first carrier network and by communicating with a firstApplication Server (AS) of the second carrier network, using a sameprotocol as used by the first CSCF node to communicate with a second ASof the first carrier network.

Returning to 410 (e.g. when the second carrier network was determined tonot be a trusted carrier), the first carrier network may handle theinbound roaming request using another procedure, such as local breakoutvia a BGCF and a circuit switched network of the first carrier networkand similar systems of the second carrier network.

FIG. 5 illustrates a component level view of a telecommunication networkdevice 500 capable of implementing the I/S-CSCFs 120 and other networkdevices of FIG. 1 . The network device 500 may, as an example, comprisea physical or virtual computer server. The network device 500 maycomprise a system memory 502 storing various executable components anddata for implementing the systems and methods 100-400 of FIGS. 1-4 . Thenetwork device 500 may further comprise processor(s) 504, a removablestorage 506, a non-removable storage 508, transceivers 510, outputdevice(s) 512, and input device(s) 514, any or all of which can becommunicatively connected via a communications bus (not shown).

In various examples, the system memory 502 is volatile (such as RAM),non-volatile (such as ROM, flash memory, etc.) or some combination ofthe two. In some examples, the processor(s) 504 is a central processingunit (CPU), a graphics processing unit (GPU), or both CPU and GPU, orany other sort of processing unit.

The network device 500 also includes additional data storage devices(removable and/or non-removable) such as, for example, magnetic disks,optical disks, or tape. Such additional storage is illustrated in FIG. 5by removable storage 506 and non-removable storage 508. The systemmemory 502, removable storage 506 and non-removable storage 508 are allexamples of non-transitory computer-readable storage media.

In some examples, the transceivers 510 include any sort of transceiversknown in the art. For example, transceivers 510 may include a radiotransceiver that performs the function of transmitting and receivingradio frequency communications. Also, or instead, the transceivers 510may include other wireless or wired connectors, such as Ethernetconnectors or near-field antennas. The transceivers 510 may facilitateconnectivity between a public network, such as a packet-switched accessnetwork (not shown), and one or more other devices of atelecommunication network.

In some examples, the output devices 512 include any sort of outputdevices known in the art, such as a display, speakers, a vibratingmechanism, or a tactile feedback mechanism. Output devices 512 alsoinclude ports for one or more peripheral devices, such as headphones,peripheral speakers, or a peripheral display.

In various examples, the input devices 514 include any sort of inputdevices known in the art. For example, the input devices 514 may includea camera, a microphone, a keyboard/keypad, or a touch-sensitive display(such as the touch-sensitive display screen described above). Akeyboard/keypad may be a push button numeric dialing pad (such as on atypical telecommunication device), a multi-key keyboard (such as aconventional QWERTY keyboard), or one or more other types of keys orbuttons, and may also include a joystick-like controller and/ordesignated navigation buttons, or the like.

Although features and/or methodological acts are described above, it isto be understood that the appended claims are not necessarily limited tothose features or acts. Rather, the features and acts described aboveare disclosed as example forms of implementing the claims.

What is claimed is:
 1. A method comprising: receiving, by a firstcarrier, an inbound roaming request from a user equipment (UE); inresponse to receiving the inbound roaming request, determining, by thefirst carrier, whether a second carrier that is a home carrier of the UEis a trusted carrier associated with the first carrier; in response todetermining that the second carrier is the trusted carrier, performingan IP Multimedia Subsystem (IMS) procedure associated with the UE atleast by: communicating, by a first call session control function (CSCF)node of the first carrier, with a first Home Subscriber Server (HSS) ofthe second carrier, using a same first protocol as used by the firstCSCF node to communicate with a second HSS of the first carrier, andcommunicating, by the first CSCF node, with a first Application Server(AS) of the second carrier, using a same second protocol as used by thefirst CSCF node to communicate with a second AS of the first carrier;and in response to determining that the second carrier is not thetrusted carrier: determining a domain name of the second carrier bycommunicating, by the first CSCF node, with an E.164 Number to URIMapping (ENUM) of the first carrier, directing, by a breakout gatewaycontrol function (BGCF) of the first carrier, the inbound roamingrequest to a circuit switch (CS) network of the first carrier, andcommunicating, by the CS of the first carrier, with a CS network of thesecond carrier and an IMS of the second carrier.
 2. The method of claim1, wherein the communicating, by the first CSCF node, with the first HSSof the second carrier includes obtaining user authentication informationassociated with the UE.
 3. The method of claim 2, wherein thecommunicating, by the first CSCF node, with the first HSS of the secondcarrier is performed over a Diameter (Cx) interface between the firstCSCF node, with the first HSS.
 4. The method of claim 1, wherein thecommunicating, by the first CSCF node, with the first HSS of the secondcarrier includes obtaining an Initial Filter Criteria (iFC).
 5. Themethod of claim 4, wherein the communicating, by the first CSCF node,with the first AS of the second carrier is performed over a IMS ServiceControl (ISC) interface between the first CSCF node, with the first ASusing the iFC.
 6. The method of claim 1, wherein the communicating, bythe first CSCF node, with the first HSS of the second carrier and thefirst AS of the second carrier bypasses one or more CSCF nodes of thesecond carrier.
 7. The method of claim 1, wherein the first CSCF nodeincludes an Interrogating-Call Session Control Function (I-CSCF) and aServing-Call Session Control Function (S-CSCF) of the first carrier. 8.A system comprising: one or more computing devices of a first carrierconfigured to perform actions comprising: receiving, by the firstcarrier, an inbound roaming request from a user equipment (UE); inresponse to receiving the inbound roaming request, determining, by thefirst carrier, whether a second carrier that is a home carrier of the UEis a trusted carrier associated with the first carrier; in response todetermining that the second carrier is the trusted carrier, performingan IP Multimedia Subsystem (IMS) procedure associated with the UE atleast by: communicating, by a first call session control function (CSCF)node of the first carrier, with a first Home Subscriber Server (HSS) ofthe second carrier, using a same first protocol as used by the firstCSCF node to communicate with a second HSS of the first carrier; and inresponse to determining that the second carrier is not the trustedcarrier: determining a domain name of the second carrier bycommunicating, by the first CSCF node, with an E.164 Number to URIMapping (ENUM) of the first carrier, directing, by a breakout gatewaycontrol function (BGCF) of the first carrier, the inbound roamingrequest to a circuit switch (CS) network of the first carrier, andcommunicating, by the CS of the first carrier, with a CS network of thesecond carrier and an IMS of the second carrier.
 9. The system of claim8, wherein the communicating, by the first CSCF node, with the HSS ofthe second carrier includes obtaining user authentication informationassociated with the UE.
 10. The system of claim 9, wherein thecommunicating, by the first CSCF node, with the first HSS of the secondcarrier is performed over a Diameter (Cx) interface between the firstCSCF node, with the first HSS.
 11. The system of claim 8, wherein thecommunicating, by the first CSCF node, with the first HSS of the secondcarrier includes obtaining an Initial Filter Criteria (iFC).
 12. Thesystem of claim 11, the actions further comprising: communicating, bythe first CSCF node, with a first Application Server (AS) of the secondcarrier, using a same second protocol as used by the first CSCF node tocommunicate with a second AS of the first carrier, wherein thecommunicating, by the first CSCF node, with the first AS of the secondcarrier is performed over a IMS Service Control (ISC) interface betweenthe first CSCF node, with the first AS using the iFC.
 13. The system ofclaim 8, the actions further comprising: communicating, by the firstCSCF node, with a first AS of the second carrier, using a same secondprotocol as used by the first CSCF node to communicate with a second ASof the first carrier, wherein the communicating, by the first CSCF node,with the first HSS of the second carrier and the first AS of the secondcarrier bypasses one or more CSCF nodes of the second carrier.
 14. Thesystem of claim 8, wherein the first CSCF node includes anInterrogating-Call Session Control Function (I-CSCF) and a Serving-CallSession Control Function (S-CSCF) of the first carrier.
 15. Anon-transitory computer-readable media storing computer-executableinstructions, which when executed by one or more processors, cause theone or more processors to perform actions comprising: receiving, by afirst carrier network, an inbound roaming request associated with a userequipment (UE); in response to receiving the inbound roaming request,determining, by the first carrier, whether second carrier network thatis a home carrier network of the UE is a trusted carrier networkassociated with the first carrier network; in response to thedetermining that the second carrier network is the trusted carriernetwork, performing a procedure associated with the UE at least by:communicating, by a first call session control function (CSCF) node ofthe first carrier network, with a first Application Server (AS) of thesecond carrier network, using an interface with a same first protocol asused by the first CSCF node to communicate with a second AS of the firstcarrier network; and in response to determining that the second carrieris not the trusted carrier: determining a domain name of the secondcarrier by communicating, by the first CSCF node, with an E.164 Numberto URI Mapping (ENUM) of the first carrier, directing, by a breakoutgateway control function (BGCF) of the first carrier, the inboundroaming request to a circuit switch (CS) network of the first carrier,and communicating, by the CS of the first carrier, with a CS network ofthe second carrier and an IMS of the second carrier.
 16. Thenon-transitory computer-readable media of claim 15, the performing theprocedure associated with the UE further performed by: communicating, bythe first CSCF, with a first Home Subscriber Server (HSS) of the secondcarrier network, using a same second protocol as used by the first CSCFnode to communicate with a second HSS of the first carrier network,wherein the communicating, by the first CSCF node, with the first HSS ofthe second carrier network includes obtaining user authentication of theUE over a Diameter (Cx) interface between the first CSCF node, with thefirst HSS.
 17. The non-transitory computer-readable media of claim 15,the performing the procedure associated with the UE further performedby: communicating, by the first CSCF, with a first HSS of the secondcarrier network, using a same second protocol as used by the first CSCFnode to communicate with a second HSS of the first carrier network,wherein the communicating, by the first CSCF node, with the first HSS ofthe second carrier network includes obtaining an Initial Filter Criteria(iFC).
 18. The non-transitory computer-readable media of claim 17,wherein the communicating, by the first CSCF node, with the first AS ofthe second carrier network is performed over a IMS Service Control (ISC)interface between the first CSCF node, with the first AS using the iFC.19. The non-transitory computer-readable media of claim 15, theperforming the procedure associated with the UE further performed by:communicating, by the first CSCF, with a first HSS of the second carriernetwork, using a same second protocol as used by the first CSCF node tocommunicate with a second HSS of the first carrier network, wherein thecommunicating, by the first CSCF node, with the first HSS of the secondcarrier network and the first AS of the second carrier network bypassesone or more CSCF nodes of the second carrier network.
 20. Thenon-transitory computer-readable media of claim 15, wherein the firstCSCF node includes an Interrogating-Call Session Control Function(I-CSCF) and a Serving-Call Session Control Function (S-CSCF) of thefirst carrier network.